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1
Q

What are the 2 types of statistics

A

Descriptive , inferential (analysed)

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2
Q

What is evidence based medicine

A

Conscientious, explicit and judicious use of current best evidence in making decisions about care of individual patients

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3
Q

What is epidemiology

A

Study of distribution and determinants of health-related states or events in specified populations and application to health problems

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4
Q

Characteristics of surveillance and descriptive studies

A

Studies distribution

One group studied, no explicit hypothesis, development of possible hypothesis

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5
Q

Analytical studies

A

Study determinants

2 or more groups
Definite hypothesis
Reject or accept

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6
Q

Experimental studies are always

A

Analytical

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7
Q

2 types of observational study

A

Descriptive and analytical

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8
Q

2 types of descriptive study

A

Ecological studies and cross-sectional surveys

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9
Q

2 types of analytical studies

A

Case-control

Cohort

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10
Q

Requirements of sample population

A

Representative, unbiased, precise

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11
Q

2 types of validity

A

Internal and external

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12
Q

What is internal validity

A

Freedom from confounding, bias or random error

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13
Q

What is external validity

A

Degree to which conclusions can be applied to the population of interest

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14
Q

2 types of error

A

Chance or bias

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15
Q

Why do chance errors happen

A

Due to sampling variation, reduces as sample size increases

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16
Q

2 types of bias

A

Selection bias or information bias

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17
Q

Reasons for selection bias

A

Study sample not representative
Group selection within study not comparable
Healthy worker effect

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18
Q

Information bias examples

A

Recall error
Observer/interviewer error
measurement error
Misclassification

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19
Q

What is prevalence

A

Absolute risk

Proportion of people with a disease

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20
Q

What is incidence

A

Absolute risk

Number of new cases within a given time frame

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21
Q

What is incidence rate ratio

A

Compares incidence rate in 2 groups

IR1/IR2 = IRR

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22
Q

What is odds ratio

A

Comparison of odds of disease in one group compared to another

Ratio of ratios

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23
Q

what is risk difference

A

Absolute risk of A - Absolute risk of B

No difference = 0

24
Q

What are person years

A

Sum of total time of everybody followed up in study

People x years

25
What is 95% confidence interval
Range within which we can be 95% certain that the true value lies
26
Wider 95% confidence interval if
Greater variation in population values | Smaller sample size
27
How to calculate 95% confidence interval
Error factor = e to the power of 2 x square root of 1/a + 1/b
28
What 95% confidence ratio suggests findings are not significant
If it spans over 1
29
Upper and lower boundary calculations
IR x ef = upper IR / ef = lower Upper-lower = x
30
What happens if 95% confidence interval spans over 1 e.g. 0.5-8
Fail to reject the null hypothesis and no statistical significance
31
Issue when comparing groups
Confounding
32
Confounding variable must influence
Both the group and the thing being tested
33
Solutions to confounding
Match important confounders Weighted average Standardised mortality ratio
34
Ecological studies key points
Identify groups of people to study (not individuals) Data on group-level characteristics Observational
35
Issues with ecological studies
``` Measurement variation Confounding Chance (random error) ```
36
Cross-sectional survey key points
Survey/series of surveys Exposure and outcome measured simultaneously Determines prevalence mainly Analysis of individuals
37
Example of ecological study
Colon cancer incidence per 100,000 women and per capita daily meat consumption
38
Example of cross-sectional survey
Effect of aircraft noise exposure on heart rate during sleep in population living near airports
39
Issues with cross-sectional survey
Sampling bias Responder/participant bias Chance (random error) Confounding
40
Advantages of cross-sectional survey
Cheap Fast Reflective of real life
41
Case control study key features
``` Always retrospective Identify group of cases and non-cases (controls) Ascertain previous exposure status Compare level of exposure in each group Analyse odds ratio ```
42
What is a nested case-control study
Collection of data from evolving outcome and exposure database of a concurrent or prospective cohort study
43
Advantages of nested case control study
Incidence rates calculated Population for sampling already defined Can collect more detailed information for a minority of participants
44
Advantages for case control study
Good for rare diseases Cheap Quick Can study multiple exposures for a single outcome
45
Issues with case control study
Selection bias Information bias (misclassification) -Non-differentiated (randomly inaccurate measurement) -Differentiated (systematic, recall bias, assessor bias, data collection errors) Confounding Chance (random error)
46
What is a cohort study
Always prospective Group individuals according to level of exposure Select outcome free individuals Ascertain outcomes for everyone Compare incidence rates for each exposure group
47
Analysis of cohort study
Odds ratio/rate ratio | Comparisons externally e.g. standardised mortality ratio or internally e.g. IRR
48
Advantages of cohort study
Enable derailed and prospective assessment of exposure, outcomes and confounders Studying a range of different outcomes, rare exposure, whether exposure precedes outcome, conditions that fluctuate with age
49
Issues in cohort study
``` Loss to follow up - differential loss, survivor bias Information bias Confounding Chance (random error) Expensive Take long time Large and resource intensive ```
50
Example of cohort study
5000 people followed up from age 55 for 10 years 2000 smokers —> 200 developed lung cancer 3000 non smokers —-> 20 developed lung cancer
51
Describing a study
``` Study design- PICO Population Intervention/exposure Comparison/control Outcome ```
52
What is SMR
Standardised mortality ratio
53
SMR equation
Observed number of deaths/ expected number of deaths
54
What bias is always present
Sampling bias Random error Also somewhat confounding
55
In what study is confounding highest
Ecological

PASS Sem2 (2 decks)

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